Method of recovering solvent employed in the separation of acetylene from gaseous mixtures



2.1sb,'496 TION F. R. BALCAR Nov. 2l, 1939.

METHOD OF RECOVERING SOLVENT EMPLOYED IN THE SEPARA OF ACETYLENE FROMGAS-EOUS MIXTURE S Filed July 50, 1937 INVENTOR. v

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Patented Nov. g1, i939 'UNITED STATE 2,180,496 METHOD or nEcovEmNGsoLvEN'r EM- PLOYED 1N THE SEPARATION LENE FROM GASEOUS MIXTURESFrederick R. Balear,

Stamford, Conn., assgnor to Air Reduction Company,

Incorporated, New

York, N. Y., a corporation of New York Application July su, 1937',sel-ini Nn. 156.4133

v claims. (c1. ceo-679) tion of suitable'solvents, for example alkylcarv bonates, ketones, ethers and esters of organic 1 0 acids. Examplesof such solvents are acetone or dimethyl ketone, methyl ethyl ketone,methyl normal propyl ketone, ethers of ethylene glycol, diethyleneglycol, di-etliyl carbonate, etc. Reference is made to United StatesPatent No. 1,854,141

to G. F. I-Iorslevwhich clearly sets forth the ideal.

qualities of a solvent suitable for use in separating `acetyleneselectively from gaseous mixtures.

Usually, the effective solvents for selective separation of acetylene-have a vapor pressure at ordinary temperatures such that substantialquantities of the solvent pass out of the absorption system with the-waste gases and the product.

-The recovery of the solvent thus withdrawn from the system is essentialin order that the costs of operation may be maintained as low aspossible.

In the absence of a method of recovering the solvent vapors, the lossesare substantial.

Solvent recovery may be effected in a number of conventionaLways, forexample, by refrigeration or by absorption in charcoal or otherabsorbent.

However, the conventional methods of solvent recovery as heretoforeknown require considerable amounts of heat or power, which represent anundesirable addition to the cost of separating acety- ,35 lene fromgaseous mixtures.

It is the object of the present inventionto provide an emcient andeconomical method of recovering solvent vapors continuously during theoperation of separating acetylene from gases.

Another object of the invention is the provision of a method whereby therecovered solvent is returned immediately to the system and the mediumemployed for recovery is likewise available for re-use. Y

I have discovered that the vapors of solvents suitable for the recoveryof acetylene from gaseous mixtures. such as those produced by thethermal decomposition of hydrocarbons, are as a rule suilicientlysoluble in hydrocarbon oils so that the re- 50 covery of such vaporsfrom the waste gas and from the acetylene product maybe accomplishedeiilciently by suitable scrubbing of the gases with such hydrocarbonoils. This operation is`particularly advantageous because of therelatively low 5E solubility of acetylene in hydrocarbon oil, so thatthe recovery of acetylene is not aiected materially by the removal ofthe solvent vapors therefrom. Consequently it is possible to separateacetylene leiciently and at the same time toavid losses of the solventeimployeci.y l

As 'a hydrocarbon oil, I prefer to se a petroleum fraction, such askerosene, or a fraction having a higher boiling point, such as a or awash oil. Anyyo'ther oil of higher or lower boiling point such as `acracked residue or an arogas oil, or fuel oil, V

matic material or one containing unsaturated materials will be effectivein` condensing the solvent vapor, provided it is not objectionablebecause of some adverse eifect due to the peculiarities of theparticular material.

In carrying out the invention, the recovery of acetylene from thegaseous mixture is conducted preferably in a cyclic manner so that theentering gaseous mixture is brought into contact with the 'solvent andthe acetylene with minor proportions of other constituents of thegaseous mixture are effectively dissolved. The solvent containing theacetylene is then subjected preferably to the action of substantiallypure acetylene which displaces other constituents dissolved in thesolvent. Thereafter the solvent is subjected to heat, so that the maiorportion ofthe acetylene is separated and withdrawn, leaving the solventin con# dition towbe returned for further treatment of the gaseousmixture. From the cycle as thus briefly outlined, waste gases willescape as theV eiiiuent from the initial step of separating acetylenefrom the gaseous acetylene recovered from rthe solvent will be withdrawnas the product of the operation. -Both the eiiluent waste vgas and theacetylene product will carry substantial proportions of solvent vapor.

This solvent vapor, which otherwise would be v lost,` is recovered byscrubbing both the emuent waste gas and the acetylene product with ahydrocarbon oil as previously described. Substantially all of thesolvent vapor is dissolved in the hydrocarbon oil, so that the efuentwaste gas can be discharged. and utilized for any and the acetyleneproduct can be stored for further use. The hydrocarbon oil containingthe dissolved solvent vapors is then delivered to a scrubber where it issubjected to contact with the entering gaseous mixture, preferably at anelevated temperature, before the gaseous mixture -is mixture, and theportion of the desired purpbse,

, delivered to the scrubberwherein the acetylene 'ylene recovered asvided with a coil I1 and losses' are thus avoided. The hydrocarbon oil,freed from the solvent vapors, may be then utilized for scrubbing theeiiiuent waste gas and the acetylene product, thus completing thecycle.`

Inasmuch as the hydrocarbon oil may possibly absorb some proportion ofhydrocarbons other than acetylene, that portion of the oil which isutilizedto f ree the acetylene product from solvent vapors is preferablytreated with steam, which ensures the separation of the undesirablehydrocarbons and avoids contamination of the acetylene product. I'hisstep is unnecessary in respect to the portion of the hydrocarbon oilwhich is employed to-free the'eiiiuent waste gas from solvent vapors.

'Ihe invention will bedescribed in more detail with reference to thedrawing, which illustrates diagrammatically an apparatus suitable forthe practice of the invention, it being understood that the drawing ismerely illustrative and that many of the details of the apparatus may bemodified.

Referring to the drawing, represents a suitable `tower provided withtrays 6 and the usual hats 1, adapted to ensure thorough contact ofgases rising through the tower with the solvent liquid ilowingdownwardly therethrough. 'I'he gaseous mixture is introduced through apipe 8,

approximately midway ofthe length of the column, and rising through theupper part of the column, is thoroughly scrubbed with the solvent sothat the acetylene is selectively removed. The eiiluent waste gasescapes through a pipe 9. The liquid solvent, continuing through thelower part of the column 5, is brought into contact with vaporsconsisting substantially of acetintroduced through a pipe I0. The effectof the acetylene is to remove constituents such as carbon dioxide, etc.,which may be dissolved during the scrubbing of the gaseous mixture in'the upper section of the column.

The liquid solvent is withdrawn through a pipeV 1 and delivered througha pump I2 and heat exchanger I3 'to the upper part o1' a column I4 whichis likewise provided with trays I5 and hats I6. 'Ihe lower partof thecolumn is prowhich is supplied with steam or other suitable heatingmedium. The heat thus applied to the liquid solvent separates theacetylene. therefrom, and the vapors rising through the column ensurethe removal of a substantial proportion of all of the acetylenedissolved in the liquid solvent. The vapors pass upwardly through aplied with water or other cooling agent by a pipe I9, the cooling agentescaping through a pipe 20. The condenser prevents the escape of some ofthe vapors of the solvent, and the acetylene product is withdrawnthrough `a pipe 2I provided with a valve 22. A portion of the acetyleneis withdrawn through a pipe 23 having a valve 24, and is delivered tothe pipe I0, and thence to the bottom of the column 5.

'I'he liquid solvent from the bottom of the column I4 is withdrawnvthrough a pipe 25 and is delivered by a pump 26 to the heat exchangerI3, where a portion of the heat is transferred to the liquid enteringthe column I4. A pipe 21 conveys the solventto a cooler 28, which may besupplied with water or other cooling agent by a pipe 29, the coolingagent escaping through a pipe 30. A pipe 3| delivers the solvent to thetop1 of the column 5, thus completing the solvent cyc e. l

hereinafter described, and.

condenser I8, which is sup- .move the solvent' vapors is delivered fromthe scrubbers 32 and 33 through pipes 42 and 43 to a pipe 44, whichconveys it to a scrubber 45 having trays 46 and hats 41.

The gaseous mixturecontaining the acetylene is introduced through a pipe48, compressed to the desired pressure in a compressor 49, and raised tothe desired temperature in a heater 50 which may be supplied with steamor other suitable heating medium through a pipe 5I. The heating mediumescapes through a. pipe 52. From the heater 50, the entering gaseousmixture is -delivered by a pipe 53 to the scrubber 45, and passesupwardly in contact with the hydrocarbon oil. The solvent vapors arethus separated and delivered through a pipe 54 to a cooler The eiiiuentwaste'gas 55 which may be supplied with water or other cooling agentthrough apipe 56, the cooling agent escaping through a pipe 51. Thencethe gaseous mixture carrying the hydrocarbon vapors enters the column 5through the pipe 8 as previously described.

A portion of the hydrocarbon oil withdrawn 81 carrying with it anyundesirable hydrocarbon vapors. The hydrocarbon oil is delivered throughapipe 68 to a cooler 69 which may be cooled with water or other suitablemedium circulating through pipes 10 and 1I. Thence the hydrocarbon oilpasses through `a pipe 12 to a 'pump 13 and is delivered through a pipe14 to the top of the scrubber 33.

In accordance with the foregoing description, it will be observed thatthe absorption of acetylene in the'solvent operates continuously as thegaseous mixture is introduced, the acetylene being dissolved andseparated and the solvent being returned for further use. A portion ofthe acetyv.

lene product is utilized to preclude carrying over other solubleconstituents such as carbon dioxide, etc., with the solvent. At the sametime, solvent vapors which may escape with the eiiluent waste gas andwith the acetylene product are effectively-separated and are returnedcontinuously to the column in which the initial separation of theacetylene is eiected. 'I'here is, therefore, substantially no loss ofsolvent in the system. Similarly, the hydrocarbon oil employed for therecovery of solvent vapors vis utilized without substantial loss' and iscontinuously circulated.

Since the volume of gasl escaping from the acetylene absorption cycle isequal in amount to the gas entering, the incoming gas will besui'llcient in volume to remove the condensed solvent from the oil,provided that the quantity of oil used is 'just sufficient to condensethe' solvent from the gaseous products yof the system under idealconditions. cess oil is necessary to eilect complete condensation oithesolvent vapors, so that ifA the incoming gas is at the sametemperature and pressurelas the gas from which the solvent has lbeencondensed, it will not be sumcient in amount to remove the solventcompletely from 'the oil. In this case; it may be necessary to heat theincoming gas to a temperature higher than that of the gases leaving theabsorption system, so that a given quantity of Qthe incoming gas canremove a greater proportion of solvent vapor from the oil. The amount ofheatrto be supplied, h owever, will be much less than would be the casein any of the conventional methods of solvent recovery.

LvIn case the acetylene absorption cycle is op'- erated atsuperatmospheric pressure, the incoming gas being pumped to thatpressure, the removal of the condensed solvent from the oil may beaccomplished advantageously by passing the incoming gas therethrough atapproximately atmospheric pressure. Since the volume of incoming gasunder these conditions is greater than the volume of gas leaving theacetylene absorber at the higher pressure. it will then be moreeffective in carrying the solvent out of the oil and returning it to thesyst'emfand the temperature of the gas need not be so high foreffec--tlve recovery ofthe solvent from the oil. acetylene in hydrocarbon oilis 'relatively low, and the volume of oil necessary to recover thesolvent from the gaseous products of the acetylene absorber yis smallcompared tothe volume of gas to be treated, the quantity of acetylenelost in this method of operation due to passing the incomingacetylenecontaining gas through the oil will, for all practicalpurposes, be negligible. u

-As an alternative, however, the oil, after having condensed the solventvapor, may be treated at a more highly elevated temperature by a smaller'quantity of another suitable gas such as nitrogen or a portion of thewaste gas itself, this other gas then being mixed with the incoming gasbefore it enters the acetylene recovery system so as to return theacetylene solvent to the system. q

The advantages of the method' as described have been set forth, andvarious changes may be made in the procedure, as well as in the detailso`f the apparatus, without departing from the invention or sacrificingany of its advantages.

I claim: I

1. In the .separation of acetylene from gaseous mixtures in which thegaseous mixture is brought into contact with a solvent 4dissolvingacetylene selectively from the gaseous mixture and `the solventcontaining dissolved acetylene. subsequently is heated to liberateacetylene and the solvent from which the acetylene is liberated isreturned for dissolving more acetylene; the improvement which comprisesheating the gaseous mixture prior to bringing it intc contact with thesolvent, scrubbing the acetylene liberated from the solvent with aliquid absorbent capable of dissolving the solvent and having a higherboiling point than the solvent, and separating'the dissolved solventfrom the liquid absorbent by scrubbing the incoming 'heated gaseousmixture therewith before sepa- In actual practice,l exacetylene andsolvent and having a capable oi ration of acetylene y 2. In theseparation' of acetylene from gaseous mixtures in which the. gaseousmixture .is brought into contact dissolving acetylene selectively fromthe gaseous mixture 'and the solvent containing dissolved acetylenesubsequently is heated to liberate Y the solvent from which theacetylene is liberated is returned for dissolving more acetylene; theimprovement which comprises heating the gaseous mixture into contactwith thesolvent, scrubbing the eiu-v ent `gas which is not dissolved bythe solvent with a liquid absorbent capable of dissolving the higherboiling point than the solvent, and separating the dissolved solventfrom lthe liquid absorbent by scrubbing the incoming heated gaseousmixture therewith before separation of acetylene from said gaseousmixture.

3. In the separation of acetylene from gaseous mixtures in which thegaseous mixtureis from said gaseous mixture.

with a solvent capable of prior to bringing it. y

brought into contact with a solvent capable of dissolving acetyleneselectively from the gaseous mixture and the solvent containingdissolved acetylene subsequently is heated to liberate acetylene and thesolvent from which the acetylene is liberated isreturned for dissolvingmore acetylene; the improvement which comprises heating the gaseousmixture prior to bringing it into contact with the solvent, scrubbingthe acetylene liberated from the solvent and the efrluent gas which isnot dissolved by the solvent with a liquid absorbent capable ofdissolving the solvent and having a higher boiling point than thesolvent, separating the dissolved solvent from the liquid absorbent byscrubbing the incoming heated gaseous mixture therewith beforeseparation of acetylene from said gaseous mixture, and returning theliquid absorbent for further use in recovering solvent.

4. In theseparation of acetylene from gaseous mixtures in which thegaseous mixture is brought irrto contact with a solvent capable ofdissolving acetylene selectively from the gaseous mixture and thesolvent containing dissolved acetylene subsequently is heated toliberate acetylene and the solvent from which the acetylene is liberatedis returned for dissolving more acetylene; the improvement whichcomprises heating the gaseous mixture prior to bringing it into contactwith the solvent, scrubbing the acetylene liberated from the solventwith a liquid absorbent capable of dissolving the solvent and having' ahigher boiling pointthan the solvent, separating the dissolved solventfrom -the liquid absorbent by scrubbing the incoming heated gaseousmixture therewith before separation of acetylene and returning .the forfurther use in recovering is returned for dissolving more acetylene; the

improvement which comprises heating the gaseous mixture prior tobringing it into contact s with the solvent, scrubbing the emuent gaswhich is not dissolved by the solvent with a liquid absorbent capable ofdissolving the solvent and having a higher boiling point than thesolvent,

soI

separating the dissolved solvent from the liquid absorbent by scrubbingthe incoming heated gaseous mixture therewith before separation oirecovering solvent.

6. Inthe separation of acetylene from gaseous 7. In the separation ofacetylene from gaseous mixtures in which the gaseous mixture is broughtFREDERICK R. BALCAR.

